Our Fresh- Water Alge. 673 
Another kind of spore, motionless, unlike the preceding, the 
zygospore or “ yokespore,” is produced only as the result of two 
cells uniting and fusing their contents, the confined mass becoming 
the zygospore. This process of coalescence, known technically as 
conjugation, occurs in the beautiful Desmids, algæ so distinct as to 
form a group by themselves and therefore not now to be entered 
upon. The process also occurs in the Spirogyras and their relatives 
common in conspicuous green masses in still waters, each mass 
composed of long threads tangled together which shine with silky 
lustre when taken out of the water giving them their English name 
of silkweeds. These spores are smooth or spiny, often studded 
with knobs or branching thorns ; they have a thick, hard case, 
resisting the drouth of summer and the cold of winter, enabling 
them to await their proper time of growth in safety. The zoospores 
are liableto confusion with certain green infusoria ganimalcules, 
the zygospores with certain similar unicellular alge as species of 
Acanthococcus, now thought to have been often mistaken in this 
country for desmid zygospores. 
A very curious kind of reproduction is that of the Vaucheria and 
its allies, the production of “ oospores,” which resemble zygospores 
in their resting-period and in their hard, shell-like case, but differ 
in formation, And if with Goebel we include the Charas among 
the alge, we are presented by them with still another mode of 
reproduction, the formation of “ nucules ” or nutlets, dark or red, 
often strikingly handsome to the naked eye when abundant in their 
little clusters on the green feathery plant, each nucule surrounded by 
its little involucre and itself chased as if by chisel with a spiral 
line winding many times round it. 
; But perhaps the most complicated of algal systems of reproduc- 
tion is that of the red algæ, to be observed in fresh water in the 
Batrachosperms, Lemaneas, ete. It may be called the cystocarpic 
system, its result being the formation of a fruit or cystocarp, filled 
with spores, often reminding one of the grains in a pomegranate 
or the seeds in a water-melon, and sometimes still more regular in 
arrangement. Remembering the sexual system as developed in 
flowering-plants requires, previous to the formation of seed, the 
Presence of the stamen and the pistil, respectively the male and 
female elements ; we look for their counterpart in these plants, and 
